Low level explosives detection in aqueous environments is challenging, in part, because the solubility of most explosives is low and saturation concentrations are hardly ever reached in open waters due to dilution. Nitroaromatic compounds (NACs), including trinitrotoluene (TNT), dinitrotoluene (DNT), and trinitrophenyl-methylnitramine (Tetryl), are the most common explosives and those which are most often found in aqueous environments. Currently, these compounds are detected using US EPA protocol SW-846 Method 8330 which involves reverse-phase HPLC with UV detection, chemiluminescence, spectrophotometric assays, immunosensors, surface enhanced Raman scattering and electrochemical methods. The current methodology, however, does not provide the required selectivity or sensitivity needed to detect these explosives, and others, at ultra low levels.
Fluorescence quenching methods, owing to their relatively low cost, efficiency, portability, high sensitivity, and ease of operation, have emerged as a preferred means of detecting NAC explosives. It is believed that the electron-deficient NACs bind to electron-rich fluorescent materials and result in fluorescence quenching by a photoinduced electron transfer (PET) mechanism. In the past decades, a wide range of small molecule fluorophores and conjugated polymers have been developed for effective NAC sensing, but most of them are applied to detect explosives either in vapor/solid phase or in organic solvents, not in aqueous environments. Moreover, the quenching of fluorophores may be interfered with by other electron-deficient compounds.
Thus, there remains a need for selective detection methods capable of detecting low levels of explosives in aqueous environments.